1. Field of the Invention
This invention relates to bar grids used in waste water intake structures. More particularly, it refers to a self cleaning static bar grid which concentrates solid effluent prior to receipt by a filter screen apparatus.
2. Description of the Prior Art
Bar grid screens used to concentrate solid particles in waste water effluent streams frequently incur the problem of solids build-up on the screen grid with the consequent loss of head and in extreme cases partially blockage of the grid so that the screen acts as a dam. Many solutions have been suggested such as in U.S. Pat. No. 2,839,197, wherein a plurality of spaced parallel flat metallic ribbons are subjected to longitudinal tension so that the load carrying capacity of the screen is increased. This type of screen permits cleaning by a simple apparatus. In U.S. Pat. No. 3,123,558, the longitudinal members are constructed to minimize elongate materials being retained on the screen. A shaking motion is imparted to the screen for advancing debris across the screen to a discharge point. In U.S. Pat. No. 3,836,463, a mechanical rake is oriented on the face of a bar grid. The rake moves up and down in response to a motor. All of these prior art patents describe bar grid screens requiring some kind of separate cleaning action on closely spaced bars located in a vertical configuration.
A self cleaning bar grid screen is needed which will concentrate solid particles from waste water effluent streams and move them into a compactor without allowing the build-up of solid debris on the grid screen.